Electro-deposition of nickel



United States Patent l ELECTRO-DEPOSITION 0F NICKEL Ulrich Francis Marx, Birmingham, England, assignor to Wilmot-Breeden Limited, Birmingham, England No Drawing. Filed Feb. 10, 1958, Ser. No. 714,051 Claims priority, application Great Britain Feb. 21, 1 957 11 Claims. (Cl. 204-49) This invention is concerned with improvements in or relating to the electro-deposition of nickel and has for its object to provide solutions for use in, and a process of, producing nickel electro-deposits, which solutions con: tain special additives for the purpose of brightening, levelling and/or relieving stresses in the resultant electrodeposits.

Brightening is the action of giving a specular or nearspecular reflection from the surface of the electro-deposit as it comes from the bath and levelling is the action of smoothing out or camouflaging the roughness or polishing lines on the steel or other surface on which the electro-deposit is laid down. Both characteristics are to be desired and will reduce or ease any subsequent buffing of the electro-deposit, or even render buffing unnecessary altogether. It is to be understood, however, that brightness is a quality greatly affected by the plating conditions, apart from the presence or absence of the additives hereinafter enumerated.

Relief of stresses in the electro-deposits as they are applied is also, as will readily be appreciated; a desirable feature, for such stresses tend to cause the nickel electro-deposits to crack and lift from the base metal. Thus, in the case of a chromium-plated steel article, wherein nickel has first been electro-deposited on the steel prior to the chromium-plating, stresses in the nickel might cause or tend to cause the composite plating to 'peel from the steel.

According to this invention we provide a nickel electro-plating bath characterised by an acidic aqueous solution of a nickel electrolyte containing dissolved therein a small proportion of one of the following derivatives of coumarin:

6-sulphamidocoumarin Coumarin bisulphite and its salts.

6-nitrocoumarin 6-aminocoumarin 6-acetamidocournarin The nickel electrolyte may be a conventional nickel plating salt, for example the sulphate or the chloride. Advantageously the bath may be Watts solution, that is to say a solution of both nickel sulphate and nickel chloride.

The invention also includes a method for the electrodeposition of nickel comprising the step of electrodepositing nickel from an aqueous acidic solution of a nickel electrolyte containing dissolved therein a small proportion of one of the above-enumerated additives.

The use of coumarin and certain of its derivatives, namely its alkyl and acyl derivatives, as additives to nickel electro-plating baths has been suggested in British patent specification No. 622,761. Of such additives the only one used in practice, and indeed the only one which not only gives reasonably satisfactory results but the cost of which is economical, is coumarin itself. As compared with coumarin itself, the derivatives thereof pro- (Dodge, JACS 1916,

posed to be used in accordance with the present invention show a number of special advantages.

Thus, for example, the derivatives in accordance with the present invention are of comparable first cost and this, coupled with their marked economy in use as com pared with coumarin itself, renders their use, overall, cheaper. As an example, the preferred compounds in accordance with our invention, namely 6-acetamidocoumarin or 6-sulphamidocoumarin, may cost as much as three times the cost of coumarin but are only consumed in one fifth the quantity, although a similar concentration is used.

Furthermore, when coumarin itself is used, it is lost from the plating bath by vaporisation, by chemical or electromechanical degradation to compounds of undetermined nature and, possibly, by incorporation in the deposited nickel. The degradation products which accumulate in the plating bath over a period of time reduce the quality of the nickel plate deposited therefrom and, accordingly, have to be removed by treating the whole bath with activated charcoal and, occasionally, with hydrogen peroxide. This inevitably entails taking the entire plating bath out of use.

On the other hand, the degradation products of the coumarin derivatives proposed by this invention, in par-I ticular 6-sulphamidocoumarin and 6-acetamidocoumarin, which are formed are much less detrimental to theprdperties of the plated deposit. Furthermore, such degradation products may be removed by pumping the plating solution through a filter bed loaded with only a rela tively small amount of charcoal and, what is more, this may be effected merely by circulation of the plating bath 7 without taking the entire bath out of production.

All the coumarin derivatives proposed in accordance with this invention give a degree of levelling. Coumarin bisulphite gives a ductile deposit, 6-nitrocou'rna rin and 6-aminocoumarin give bright deposits which tend tobe highly stressedand, therefore, may exhibit crazing, while 6-sulphamidocoumarin and 6-acetamidocoumarin both givebright and ductile deposits and are preferred. 'The depositsjobtained by the use of the 6- sulphamido'and,6 acetamido derivatives are more or less equally ductile; but the former compound has less valuable levelling properties and the latter compound has a narrower bright plating range.

Examples of nickel-electroplating baths and their use according to this invention are given below by way of illustration, the bath in each case being basically Watts solution of the following composition:

G. per litre NiSO .6H O 250 NiC1 .6H O 45 3 3 30 the balance being water.

Example 1 6-sulphamidocoumarin is employed as the additive at a concentration between 0.01 g. per litre and saturation at the plating temperature, preferably between 0.05 and 2.5 g. per litre, and most advantageously between 0.25 and 0.5 g. per litre. Plating may be carriedlont at a pH of 2 to 6, and preferably 4 to 5, and at a temperature of 45 C. to 65 C., and preferably about 55 C. The current density may be 10 to 100 amps. per square foot, and preferably 40 to a.s.f. Bright deposits are obtainable.

Example 2 The coumarin bisulphite compound (which has also been called hydrocoumarin sulphonate) prepared as described by Dodge, JACS 1916, 38, 446 is employed as the additive, the concentration of its sodium or potassium Patented Nov. 22, 1960 salt in the bath being 0.01 to 2.5 g. per litre, and most advantageously between 0.25 and 0.50 g. per litre. Pating may be carried out at H 4, 55 C., using a current density of 40 a.s.f. to obtain semi-bright deposits.

Examples 3 to 5 The following additives may be employed at the concentrations stated:

In each case plating may be carried out at 55 0., pH 4, employing a current density of 40 a.s.f.

The propontions and plating conditions in the examples are given by way of illustration and should not be regarded as limitative of the scope of my invention.

I claim:

1. A process for the electro-deposition of nickel comprising the step of electro-depositing nickel from an acidic aqueous solution of a nickel electrolyte containing dissolved therein a small proportion of a coumarin derivative selected from the class consisting of 6-sulphamidocoumarin, coumarin bisulphite, and salts thereof, fi-nitrocoumarin, 6-aminocoumarin and fi-acetamidocoumarin, said proportion being such as to confer enhanced levelling properties on said solution.

2. A process for the electro-deposition of nickel comprising the step of electro-depositing nickel from an acidic aqueous solution of a nickel electrolyte containing dissolved therein a small proportion of 6-sulphamidocoumarin, said proportion being such as to confer enhanced levelling properties on said solution.

3. A process for the electro-deposition of nickel comprising the step of electro-depositing nickel from an acidic aqueous solution of a nickel electrolyte contatining dissolved therein an amount of 6-sulphamidocoumarin between 0.01 gram per litre and its saturation figure.

4. A process for the electro-deposition of nickel comprising the step .of electro-depositing nickel from an acidic aqueous solution of a nickel electrolyte containing dissolved therein a small proportion of G-acetamidocoumarin, said proportion being such as to confer enhanced levelling properties on said solution.

5. A process for the electro-deposition of nickel comprising the step of electro-depositing nickel from an acidic aqueous solution of a nickel electrolyte containing dissolved therein an amount of 6-acetamidocoumarin between 0.01 gram per litre and its saturation figure.

6. A process as claimed in claim 1, wherein said derivative is a coumarin bisulphite and is present in said solution in a concentration between 0.01 and 2.5 gram per litre.

7. A process as claimed in claim 1, wherein said derivative is 6-nitrocoumarin and is present in said solution in a concentration between 0.002 gram per litre and saturation.

8. A process as claimed in claim 1, wherein said derivative is 6-aminocournarin and is present in said solu tion in a concentration between 0.002 and 2.5 gram per litre.

9. A bath for the electro-deposition of nickel comprising an acidic aqueous solution of a nickel electrolyte containing dissolved therein a small proportion of a coumarin derivative selected from the class consisting of -sulphamidocoumarin, coumarin bisulphite and salts thereof, 6-nitrocoumarin, 6-aminocoumarin and 6-acetamidocournarin, said proportion being such as to confer enhanced levelling properties on said bath.

10. A bath for the electro-deposition of nickel comprising an acidic aqueous solution of a nickel electrolyte containing dissolved therein an amount of 6-sulphamidocoumarin between 0.01 gram per litre and its saturation figure.

11. A bath for the electro-deposition of nickel comprising an acidic aqueous solution of a nickel electrolyte containing dissolved therein an amount of 6-acetamidocoumarin between 0.01 gram per litre and its saturation figure.

References Cited in the file of this patent UNITED STATES PATENTS 2,635,076 Du Rose Apr. 14, 1953 2,694,041 Brown Nov. 9, 1954 2,840,517 Faust et a1 June 24, 1958 

1. A PROCESS FOR THE ELECTRO-DEPOSITION OF NICKEL COMPRISING THE STEP OF ELECTRO-DEPOSITING NICKEL AN ACIDIC AQUEOUS SOLUTION OF A NICKEL ELECTROLYTE CONTAINING DISSOLVED THEREIN A SMALL PROPORTION OF A COUMARIN DERIVATIVE SELECTED FROM THE CLASS CONSISTING OF 6-SULPHAMIDOCOUMARIN, COUMARIN BISULPHITE, AND SALTS THEREOF, 6-NITROCOUMARIN, 6-AMINOCOUMARIN AND 6-ACETAMIDOCOUMARIN, SAID PROPORTION BEING SUCH AS TO CONFER ENHANCED LEVELLING PROPERTIES ON SAID SOLUTION. 